This invention relates to electrochemical cells. Most particularly, it relates to electrochemical cells having an oxidizable active anode material, a solid metallic cathode current collector, and a covalent inorganic oxyhalide or thiohalide as the solvent for the electrolytic solution.
Modern technology has placed increased emphasis on producing an electrochemical power source having improved reliability, light weight, small size, high power and long life. Power sources meeting these requirements find ready civilian and military applications in portable communications systems, entertainment products, emergency lights, and portable electronic devices, such as wristwatches and hearing aids. An inexpensive, lightweight, high power, reliable power source would be of great value for use, for example, with portable radios or television sets.
Various high-voltage, high-energy density electrochemical cells have been the subject of recent investigation. Much of the work in this area has been involved with electrochemical cells having negative electrodes comprising highly reactive metals such as lithium.
Work on electrolytes for lithium-based electrochemical power sources has progressed generally along two major lines: high temperature, inorganic molten salt electrolytes and organic solvent-based electrolytes. A cell which utilizes a molten salt electrolyte provides a chemically stable system in which strong oxidants such as chlorine can be used as cathodes. For example, a molten salt cell utilizing a lithium anode and chlorine cathode provides exceptionally high energy and power density making development of a practical cell with these materials of particular interest. The molten salt lithium/chlorine cell (having a lithium anode, chlorine cathode and molten salt, typically lithium chloride, electrolyte) has many characteristics desirable in a high performance electrochemical cell. The anode is highly electropositive, and the cathode is highly electronegative. The equivalent weight of the reaction product is low and the anode, cathode and electrolyte conductivities are high. Nevertheless, these cells have severe problems. The temperature range of operation, which for the lithium chloride electrolyte is 450.degree. C to 650.degree. C, necessitates heating systems and insulation that increase cell cost, weight and complexity. To collect and store the chlorine evolved in rechargeable cells at these high temperatures, auxiliary systems are needed. In addition, there are few materials that can withstand, for extended periods of time, the attack of molten lithium, chlorine and molten lithium chloride at these temperatures; therefore, the operating lifetime of these cells is relatively short, typically 20 to 30 minutes. The measured and theoretical open circuit voltage of these high temperature cells is about 3.5 volts, although approximately 4 volts are theoretically obtainable at 25.degree. C (at higher temperatures the potential is lower because of the energy charge in the overall cell reaction).
In parallel with the development of lithium cells with molten salt electrolytes, lithium cells with nonhydroxylic organic solvents have been developed. These cells have been called "organic electrolyte cells" although typically they employ electrolytes consisting of inorganic salts in organic solvents. Cells of this type have the advantage of being operable at room temperature; however, chlorine itself and other strong oxidants cannot be used as the cathode depolarizer with these solvents since the solvents are oxidized by chlorine. Therefore, cells of this type will not provide an energy density as high as a lithium/chlorine cell.
In application Ser. No. 342,233, filed Mar. 16, 1973, a continuation-in-part application of application Ser. No. 131,530 filed Apr. 5, 1971, now abandoned, there is described an electrochemical cell having an active anode material selected from a specific group of materials, including lithium, a halogen or metal halide active cathode material, and an electrolyte containing phosphorus oxychloride as the solvent material and a solute, selected from a wide range of materials, dissolved in the phosphorus oxychloride. The present invention is related to the invention described in the aforementioned application in that the same anodic, solvent and solute materials can be utilized in the present invention; however, this invention relates to the use of such materials with different cathode materials which cause, in conjunction with the oxidizable anode materials, the solvent material to be electrochemically reduced during operation of the cell.